Sensing circuit

The sensing circuit is used in an Asymmetric Digital Subscriber Line (ADSL) transmission system to detect a wave signal with a predetermined shape in an input signal (IN1/IN2) transmitted over the system and applied to an input terminal (IN1/IN2) of the sensing circuit. It includes two branches with a correlated double sampling circuit (CDS1/CDS2), a counter circuit (C1/C2) and a comparator circuit (CMP1/CMP2) coupled in series. An input (IN1/IN2) of the correlated double sampling circuit of each branch is coupled to the input of the sensing circuit and an output of the comparator circuits is coupled to an output terminal (OUT) of the sensing circuit via an OR-ing circuit. The correlated double sampling circuits are adapted to provide a sampled signal and the counter circuits count the number of pulses of the sampled signals. The thus obtained count values are in the comparators are compared with a predetermined value corresponding with the count value which should be obtained when the input signal is a, possibly distorted, signal with the above mentioned predetermined shape. The sensing circuit is clocked by two clock signals, one for each branch, which are in quadrature.